Calculate the concrete volume, cement bags, sand and aggregate needed for a concrete slab. Enter your slab dimensions, mix ratio and waste allowance for a practical material estimate.
Calculate Concrete for Your Slab
How the Concrete Slab Calculator Works
The calculator starts with the slab's length, width and thickness. These dimensions determine the slab area and wet concrete volume.
Length × Width
Length × Width × Thickness
The calculator then applies your selected waste allowance. For the material estimate, the wet concrete volume is multiplied by a dry volume factor of 1.54. This accounts for the loose material volume needed to produce the finished concrete volume.
Wet Concrete Volume × 1.54 × (1 + Waste %)
The selected concrete mix ratio divides the dry material volume between cement, sand and aggregate.
Concrete Mix Ratio Guide
| Mix Ratio | Cement | Sand | Aggregate | Typical Use |
|---|---|---|---|---|
| 1:1.5:3 | 1 part | 1.5 parts | 3 parts | Higher cement content concrete |
| 1:2:3 | 1 part | 2 parts | 3 parts | General concrete work |
| 1:2:4 | 1 part | 2 parts | 4 parts | General construction estimates |
| 1:3:6 | 1 part | 3 parts | 6 parts | Lean concrete applications |
Mix ratios are general estimating ratios. Structural slabs should follow the concrete specification provided by the project engineer or applicable building standard.
Example: Concrete Slab Calculation
Suppose a slab is 6 m long, 4 m wide and 150 mm thick.
With a 5% waste allowance, the calculator increases the quantity used for material planning. The final cement, sand and aggregate quantities depend on the selected mix ratio and cement bag size.
Concrete Slab Calculator FAQs
Multiply the slab length by its width and thickness. Convert all dimensions to the same unit first. The result gives the wet concrete volume. Add a suitable waste allowance when ordering materials.
Convert 100 mm to 0.1 m, then multiply the slab length, width and 0.1 m thickness. For example, a 5 m × 4 m slab requires 5 × 4 × 0.1 = 2 m3 of wet concrete before waste.
A 5% allowance is a common starting point for estimates. Site access, formwork, uneven ground and placement conditions affect the amount of extra concrete required.
The number depends on the concrete volume, mix ratio, cement density and bag size. Enter these values in the calculator to estimate the required number of bags.
Yes. Concrete volume is directly related to thickness. Increasing slab thickness increases the amount of concrete required for the same length and width.
No. It estimates concrete and basic material quantities. Structural slab thickness, reinforcement, concrete strength, loading and support conditions require a proper structural design.